Protocol for measuring stressor effects and growth rates of microalgae and seaweeds at organismic and populational levels

Stress and growth rates in microalgae and seaweeds are often evaluated by different methods, making the resulting data often incomparable. This poses significant challenges for basic and applied phycological research and algae industry development. To address this issue, we provide a protocol with quantitative definitions and mathematical formulae for assessing algal stress on biomass productivity in organisms and populations. Our purpose with this protocol is to offer a mathematical model to quantify and compare stressors and strains across algal taxa, going beyond qualitative and species-specific approaches. We have applied our protocol to analyze data from studies on Ulva lactuca L. growth under thermal stress and nutrient limitation to demonstrate our protocol's utility and easiness of use. We also present a new and unified perspective for algal stress ecophysiology.